The vehicle steering device is configured to use an electric motor and assist the driver with the electromotive torque of the electric motor in order to reduce the driver's steering force. The electromotive torque is increased or decreased according to the speed of the vehicle.
When the vehicle receives a strong crosswind while the vehicle is travelling, or when the vehicle travels on a rutted road, vehicle behavior such as deflection into directions away from a target travel line can occur. Therefore, the vehicle steering device detects the vehicle behavior based on the yaw rate, the lateral acceleration, and the like, and generates steering reaction torque (for restraining the vehicle behavior) based on the detected value(s). In order to address problems such as failure in each sensor arranged for detecting the yaw rate, the lateral acceleration, and the like, an upper-limit value of the steering reaction torque is determined, and a provision is made for preventing occurrence of a steering reaction torque which exceeds the upper-limit value (see Patent Literature 1, etc.).